1. Field of the Invention
The invention relates to a structure for cooling an internal combustion engine, for example, of an automobile, with cooling water.
2. Description of the Related Art
In an internal combustion engine, water jackets for causing a flow of a coolant (cooling water) therethrough are provided at a cylinder block side and a cylinder head side. A water jacket of the cylinder block (referred to hereinbelow simply as “water jacket”) is provided so as to surround a cylinder bore wall. In the water jacket, cooling water pumped by a water pump is introduced from a cooling water introducing port formed in a wall portion of the cylinder block. The cooling water introducing port is formed, for example, on one end side in the cylinder bore row direction of the cylinder block. The flow of cooling water introduced from the cooling water introducing port cools the cylinder bore wall heated by heat from the combustion chambers.
The water jacket of the cylinder head is provided mainly on the periphery of combustion chambers or on the periphery of exhaust ports. The water jacket of the cylinder head communicates with the water jacket of the cylinder block, and the cooling water from the water jacket of the cylinder block flows into the water jacket of the cylinder head. In this case, the cooling water from the cylinder block side flows to the cylinder head side via gasket holes (openings) formed in a cylinder head gasket introduced between the cylinder block and cylinder head.
In the related art, for example, Japanese Patent Application Publication No. 2006-90193 (JP-A-2006-90193) discloses a cooling structure of an internal combustion engine in which cooling water introduced from a cooling water introducing port formed in one end side of a cylinder block branches to an intake side (intake side of the internal combustion engine) and exhaust side (exhaust side of the internal combustion engine) of the water jacket and cools the cylinder bore wall. JP-A-2006-90193 indicates that a spacer that partitions the water jacket into an inner passage and an outer passage is provided in the water jacket to inhibit an overcooling phenomenon in a portion in the vicinity of the cooling water introducing port in the cylinder bore wall. Furthermore, it is indicated that a regulation portion (closing portion) that regulates the flow of cooling water from the cooling water introducing port to the inner passage from an upper or lower end portion of the spacer is provided in a portion of the spacer that faces the cooling water introducing port.
However, in the above-described cooling structure of an internal combustion engine, the flow rate of cooling water supplied to the exhaust side has to be made larger than the flow rate of cooling water supplied to the intake side of the water jacket in order to obtain a uniform temperature distribution in the portion of the cylinder bore wall on the intake side and the portion thereof on the exhaust side. In the cooling structure described in JP-A-2006-90193, the flow rate of cooling water supplied to the intake side and the flow rate of cooling water supplied to the exhaust side may be adjusted by adjusting gaps (flow channel surface areas) on the left side and right side of the regulation portion provided at the spacer. The flow rate of cooling water to the exhaust side may be increased over that to the intake side by setting a gap (flow channel surface area) that introduces the cooling water to the exhaust side larger than the gap (flow channel surface area) that introduces the cooling water to the intake side.
However, in the cooling structure described in JP-A-2006-90193, the flow rate of cooling water supplied to the exhaust side decreases because of a structure in which the cooling water supplied to the water jacket of the cylinder head is divided between the cooling water introducing port and regulation portion. This will be described in greater detail below by using a schematic view in FIG. 9.
As shown in FIG. 9, the cooling water introduced from the cooling water introducing port a branches to cooling water supplied to the water jacket of the cylinder block and cooling water supplied to the water jacket of the cylinder head via a gasket head d. Where the cooling water flow rate from the cooling water introducing port a is denoted by Qa and the cooling water flow rate to the water jacket of the cylinder head is denoted by Qd, the flow rate of cooling water supplied to the water jacket of the cylinder block will be [Qa−Qd]. The cooling water flow rate Qd to the water jacket of the cylinder head is adjusted by setting an opening surface area Sd of the gasket head d.
Then, the cooling water supplied to the water jacket of the cylinder block branches to cooling water supplied to a portion b of the cylinder block on the exhaust side and cooling water supplied to a portion c on the intake side correspondingly to flow channel surface areas Sb and Sc that guide the cooling water to the exhaust side and intake side on both sides of the above-described regulation portion. Therefore, the cooling water flow rate Qb to the portion b on the exhaust side is set to a flow rate obtained by subtracting the cooling water flow rate Qd to the water jacket of the cylinder head and the cooling water flow rate Qc to the portion c on the intake side from the cooling water flow rate Qa from the cooling water introducing port a. In other words, the relationship [Qb=(Qa−Qd)−Qc] is satisfied.
Here, a predetermined flow rate has to be reserved for the cooling water flow rate Qd to the water jacket of the cylinder head. Therefore, in a case where a large cooling water flow rate Qd has to be ensured, a state may occur in which the cooling water flow rate Qb to the portion b on the exhaust side is insufficient. As a result, there is a concern that cooling of the portion of the cylinder bore wall on the exhaust side (in particular, the upper portion in the vicinity of the combustion chamber) will be insufficient.
Meanwhile, in order to increase the cooling water flow rate Qb to the portion b on the exhaust side, the cooling water flow rate Qa from the cooling water introducing port a may be increased or the cooling water flow rate Qc to the portion c on the intake side may be reduced. However, in the cooling structure described in JP-A-2006-90193, even if the cooling water flow rate Qa from the cooling water introducing port a is increased, the degree of contribution to the increase of the cooling water flow rate Qb to the portion b on the exhaust side is decreased because the cooling water flow rate Qd to the water jacket of the cylinder head also increases. Furthermore, even if the cooling water flow rate Qc to the portion c on the intake side is reduced, the degree of contribution to the increase of the cooling water flow rate Qb to the portion b on the exhaust side is decreased because the cooling water flow rate Qd to the water jacket of the cylinder head increases. In other words, the increase of the cooling water flow rate Qa from the cooling water introducing port a or the decrease in the cooling water flow rate Qc to the portion c on the intake side do not directly contribute to the increase in the cooling water flow rate Qb to the portion b on the exhaust side and, therefore, a state may occur in which the cooling water flow rate Qb to the portion b on the exhaust side is insufficient.